Drilling Method and Apparatus

Abstract

A method of locating a drilling apparatus and/or a borehole in a subterranean region. The method may include the steps of transmitting seismic waves into the subterranean region during a subterranean drilling operation, the seismic waves being transmitted from a location remote from the drilling apparatus, detecting a seismic response from the drilling apparatus or borehole, and comparing the detected response with predetermined seismic survey data of the subterranean region to determine the location of the apparatus or borehole.

We claim: 
     
         1 . A method of locating a drilling apparatus and/or a borehole in a subterranean region, comprising the steps of:
 (A) transmitting seismic waves into the subterranean region during a subterranean drilling operation, the seismic waves being transmitted from a location remote from said drilling apparatus;   (B) detecting a seismic response from said drilling apparatus or borehole; and   (C) comparing said detected response with predetermined seismic survey data of said subterranean region to determine the location of said apparatus or borehole.   
     
     
         2 . A method as claimed in  claim 1 , wherein the seismic waves are received at a location remote from said drilling apparatus or borehole. 
     
     
         3 . A method as claimed in  claim 1 , wherein the seismic waves are transmitted from the surface of the subterranean region. 
     
     
         4 . A method as claimed in  claim 1 , wherein the seismic waves are transmitted into a well-bore extending from the surface of the subterranean region to a distal location of said drilling apparatus. 
     
     
         5 . A method as claimed in  claim 1 , wherein a seismic data set is created, preferably during drilling, by detecting a seismic response in the form of at least one of the following:
 (i) seeking/detecting prismatic waves caused by the seismic waves reflecting from geological boundaries within said region and the outer surface of the well-bore formed during the drilling operation;   (ii) seeking/detecting diffracted waves generated, for example by reflections, from the point or points at which the well-bore intersects (passes through) geological boundaries;   (iii) reflections from the bottom of the bore hole;   (iv) seismic energy transmitted into the borehole at the surface and transported into the subsurface along the borehole and radiating back to remote receivers (e.g. at the earth surface) through the subsurface strata carrying information about the position of the drill bit and the borehole; and/or   (v) wave signals associated with reflections and/or refractions caused by a difference in acoustic impedance of the well-bore and the acoustic impedance of the subterranean strata surrounding the wellbore.   
     
     
         6 . A method as claimed in  claim 1 , wherein the step of comparing said detected seismic response comprises:
 creating a seismic data-set by seeking prismatic waves generated by reflections from geological boundaries within said region and a well-bore formed during the drilling operation and/or seeking diffracted waves generated by reflections from a point of intersection of the well-bore and a geological boundary; and   subtracting said seismic data set from predetermined seismic survey data in the form of a reference seismic data set wherein the reference seismic data-set is one of a data set determined before drilling or a previous seismic data set created during drilling.   
     
     
         7 . A method as claimed in  claim 6 , wherein the step of comparing said detected response comprises the additional step of:
 seeking wave signals associated with reflections and/or refractions caused by a difference in acoustic impedance of the well-bore and the acoustic impedance of the subterranean strata surrounding the well-bore.   
     
     
         8 . (canceled) 
     
     
         9 . A method as claimed in  claim 1 , wherein the location of the drilling apparatus is determined by subtracting the detected seismic response from the transmitted seismic waves from the predetermined seismic survey data. 
     
     
         10 . A method as claimed in  claim 1 , wherein a data processor is configured to receive the predetermined survey data and to compare said data with detected response data from said transmitted seismic waves. 
     
     
         11 . A method as claimed in  claim 1 , being used for real-time monitoring of a subterranean drilling operation, wherein step (C) is used to plot a path of the drilling operation through a drilled region. 
     
     
         12 . A method as claimed in  claim 11 , wherein the seismic waves are introduced into an open end of the well-bore such that the well-bore is a seismic transmitter. 
     
     
         13 . A method as claimed in  claim 1 , being used for determining an intersection of a first well-bore and a second well-bore in a subterranean region. 
     
     
         14 . A relief well drilling method in a subterranean region using a drilling apparatus with a drill bit, the method comprising: using the method of  claim 1  to determine the location of the drill bit and directing the drill bit in response to said determined location in order that the drill bit will intersect an existing well-bore proximate a casing shoe thereof. 
     
     
         15 . A method as claimed in  claim 14 , wherein the predetermined seismic survey data is data generated by means of a mathematical model of the expected geological conditions within the subterranean region. 
     
     
         16 . A method as claimed in  claim 1  wherein a contrast gas or fluid is introduced into the wellbore to increase the reflectivity of the wellbore. 
     
     
         17 . A subterranean drill monitoring apparatus comprising:
 at least one seismic transmitter arranged to transmit seismic waves into a subterranean region from a position remote from a subterranean drill;   a plurality of seismic detectors arranged to detect a reflected and/or diffracted response from said seismic transmitter;   a processing apparatus arranged to carry out a method as claimed in  claim 1 ; and   a display means arranged to output a visualisation of the location of the subterranean drill.   
     
     
         18 . A subterranean drilling control apparatus as claimed in  claim 17 , wherein the processor is arranged to display on said display apparatus the path and instantaneous position of the subterranean drilling apparatus through and in the subterranean region. 
     
     
         19 . A computer program product comprising computer implementable instructions for causing a programmable computer to carry out the method according to  claim 1 . 
     
     
         20 . A method as claimed in  claim 2 , wherein the seismic waves are received at a location generally above the drilling apparatus and/or borehole, and on the surface of the subterranean region. 
     
     
         21 . A method as claimed in  claim 7 , wherein the step of comparing said detected response comprises amplifying said signals to determine the position of the drilling apparatus.